Hydrocarbons, such as fossil fuels (e.g. oil) and natural gas, are extracted from underground wellbores extending deeply below the surface using complex machinery and explosive devices. Once the wellbore is established by placement of cases after drilling, a perforating gun assembly, or train or string of multiple perforating gun assemblies, are lowered into the wellbore, and positioned adjacent one or more hydrocarbon reservoirs in underground formations. With reference to FIG. 1, a typical perforating gun assembly 40, (shown herein as a tubing conveyed perforating gun commercially available from DYNAenergetics GmbH & Co. KG), is depicted in which explosive/perforating charges 46, typically shaped, hollow or projectile charges, may be ignited to create holes in the casing and to blast through the formation so that the hydrocarbons can flow through the casing. As shown in the embodiment of FIG. 1, the perforating gun assembly 40 includes a gun casing or carrier or housing 48, within which various components are connected, (“connected” means screwed, abutted, snap-fit and/or otherwise assembled). At one end of the perforating gun assembly 40 of FIG. 1, a firing head 41 houses a piston 42 and a percussion initiator 10. The firing head 41 is connected to a top sub 45, and the top sub 45 houses a booster 43 and a detonating cord 44. The top sub 45 is connected to the gun housing 48, which houses an inner charge tube, strip or carrying device 47, which houses one or more of the charges 46. The detonating cord 44 makes a connection with each of the charge(s) 46. Between the firing head 41 and a tandem sub, one or multiple time delay subs may be positioned.
Once the perforating gun(s) is properly positioned, the piston 42 is accelerated by hydraulic pressure or mechanical impact, which in turn initiates the percussion initiator 10, which initiates the booster 43 to initiate the detonating cord 44, which detonates the shaped charges 46 to penetrate/perforate the casing and thereby allow formation fluids to flow through the perforations thus formed and into a production string.
In another assembly of the prior art as shown in FIG. 2, the firing head 41 that is preferably used between perforating gun assemblies and connected using a detonating cord and booster (as shown, for instance in FIG. 1), houses an alignment insert 4 on one end to which a firing pin housing 3 is connected. The firing pin housing 3 houses a firing pin 2 and is connected to an igniter support 6, which in turn houses an igniter or energetic material 5. In this assembly, initiation of the booster (not shown in FIG. 2) is used to accelerate the firing pin 2, which in turn initiates the igniter 5, which will either initiate the booster to initiate the detonating cord which detonates shaped charges in an adjacent gun or will initiate a time delay which activates one perforating gun assembly in the string of connected guns.
Advances in the art of initiating percussion initiators, particularly useful between a first perforating gun assembly and an adjacent perforating gun assembly (or multiples thereof) are constantly sought. In particular, assemblies according to the ballistic transfer module described herein improve percussion initiation, which results in improved reliability while decreasing complexity of the system, as well as lowering the cost to manufacture and assemble the perforating gun assemblies.